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(p200300d82f23a200bee782450bf42c78.dip0.t-ipconnect.de. [2003:d8:2f23:a200:bee7:8245:bf4:2c78]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454dd54c512sm38402825e9.37.2025.07.10.23.41.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Jul 2025 23:41:47 -0700 (PDT) Message-ID: Date: Fri, 11 Jul 2025 08:41:46 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: move unrelated code out of __split_unmapped_folio() To: Zi Yan , Balbir Singh , linux-mm@kvack.org Cc: Andrew Morton , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , linux-kernel@vger.kernel.org References: <20250711030259.3574392-1-ziy@nvidia.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250711030259.3574392-1-ziy@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11.07.25 05:02, Zi Yan wrote: > remap(), folio_ref_unfreeze(), lru_add_split_folio() are not related to > splitting unmapped folio operations. Move them out to the caller, so that > __split_unmapped_folio() only splits unmapped folios. This makes > __split_unmapped_folio() reusable. > > Convert VM_BUG_ON(mapping) to use VM_WARN_ON_ONCE_FOLIO(). > > Signed-off-by: Zi Yan > --- > Based on the prior discussion[1], this patch makes > __split_unmapped_folio() reusable for splitting unmapped folios without > adding a new boolean unmapped parameter to guard mapping related code. > > Another potential benefit is that __split_unmapped_folio() could be > called on after-split folios by __folio_split() to perform new split > methods. For example, at deferred split time, unmapped subpages can > scatter arbitrarily within a large folio, neither uniform nor non-uniform > split can maximize after-split folio orders for mapped subpages. > Hopefully, performing __split_unmapped_folio() multiple times can > achieve the optimal split result. > > It passed mm selftests. > > [1] https://lore.kernel.org/linux-mm/94D8C1A4-780C-4BEC-A336-7D3613B54845@nvidia.com/ > --- > > mm/huge_memory.c | 275 ++++++++++++++++++++++++----------------------- > 1 file changed, 139 insertions(+), 136 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 3eb1c34be601..d97145dfa6c8 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3396,10 +3396,6 @@ static void __split_folio_to_order(struct folio *folio, int old_order, > * order - 1 to new_order). > * @split_at: in buddy allocator like split, the folio containing @split_at > * will be split until its order becomes @new_order. > - * @lock_at: the folio containing @lock_at is left locked for caller. > - * @list: the after split folios will be added to @list if it is not NULL, > - * otherwise to LRU lists. > - * @end: the end of the file @folio maps to. -1 if @folio is anonymous memory. > * @xas: xa_state pointing to folio->mapping->i_pages and locked by caller > * @mapping: @folio->mapping > * @uniform_split: if the split is uniform or not (buddy allocator like split) > @@ -3425,51 +3421,27 @@ static void __split_folio_to_order(struct folio *folio, int old_order, > * @page, which is split in next for loop. > * > * After splitting, the caller's folio reference will be transferred to the > - * folio containing @page. The other folios may be freed if they are not mapped. > - * > - * In terms of locking, after splitting, > - * 1. uniform split leaves @page (or the folio contains it) locked; > - * 2. buddy allocator like (non-uniform) split leaves @folio locked. > - * > + * folio containing @page. The caller needs to unlock and/or free after-split > + * folios if necessary. > * > * For !uniform_split, when -ENOMEM is returned, the original folio might be > * split. The caller needs to check the input folio. > */ > static int __split_unmapped_folio(struct folio *folio, int new_order, > - struct page *split_at, struct page *lock_at, > - struct list_head *list, pgoff_t end, > - struct xa_state *xas, struct address_space *mapping, > - bool uniform_split) > + struct page *split_at, struct xa_state *xas, > + struct address_space *mapping, > + bool uniform_split) Use two-tabs indent please (like we already do, I assume). [...] > @@ -3706,11 +3599,14 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > { > struct deferred_split *ds_queue = get_deferred_split_queue(folio); > XA_STATE(xas, &folio->mapping->i_pages, folio->index); > + struct folio *next_folio = folio_next(folio); > bool is_anon = folio_test_anon(folio); > struct address_space *mapping = NULL; > struct anon_vma *anon_vma = NULL; > int order = folio_order(folio); > + struct folio *new_folio, *next; > int extra_pins, ret; > + int nr_shmem_dropped = 0; > pgoff_t end; > bool is_hzp; > > @@ -3833,13 +3729,18 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > */ > xas_lock(&xas); > xas_reset(&xas); > - if (xas_load(&xas) != folio) > + if (xas_load(&xas) != folio) { > + ret = -EAGAIN; > goto fail; > + } > } > > /* Prevent deferred_split_scan() touching ->_refcount */ > spin_lock(&ds_queue->split_queue_lock); > if (folio_ref_freeze(folio, 1 + extra_pins)) { > + struct address_space *swap_cache = NULL; > + struct lruvec *lruvec; > + > if (folio_order(folio) > 1 && > !list_empty(&folio->_deferred_list)) { > ds_queue->split_queue_len--; > @@ -3873,18 +3774,120 @@ static int __folio_split(struct folio *folio, unsigned int new_order, > } > } > > - ret = __split_unmapped_folio(folio, new_order, > - split_at, lock_at, list, end, &xas, mapping, > - uniform_split); > + if (folio_test_swapcache(folio)) { > + if (mapping) { > + VM_WARN_ON_ONCE_FOLIO(mapping, folio); > + ret = -EINVAL; > + goto fail; > + } > + > + /* > + * a swapcache folio can only be uniformly split to > + * order-0 > + */ > + if (!uniform_split || new_order != 0) { > + ret = -EINVAL; > + goto fail; > + } > + > + swap_cache = swap_address_space(folio->swap); > + xa_lock(&swap_cache->i_pages); > + } > + > + /* lock lru list/PageCompound, ref frozen by page_ref_freeze */ > + lruvec = folio_lruvec_lock(folio); > + > + ret = __split_unmapped_folio(folio, new_order, split_at, &xas, > + mapping, uniform_split); > + > + /* > + * Unfreeze after-split folios and put them back to the right > + * list. @folio should be kept frozon until page cache entries > + * are updated with all the other after-split folios to prevent > + * others seeing stale page cache entries. > + */ > + for (new_folio = folio_next(folio); new_folio != next_folio; > + new_folio = next) { > + next = folio_next(new_folio); > + > + folio_ref_unfreeze( > + new_folio, > + 1 + ((mapping || swap_cache) ? > + folio_nr_pages(new_folio) : > + 0)); While we are at it, is a way to make this look less than an artistic masterpiece? :) expected_refs = ... folio_ref_unfreeze(new_folio, expected_refs). Can we already make use of folio_expected_ref_count() at that point? Mapcount should be 0 and the folio should be properly setup (e.g., anon, swapcache) IIRC. So maybe expected_refs = folio_expected_ref_count(new_folio) + 1; folio_ref_unfreeze(new_folio, expected_refs). Would do? > + > + lru_add_split_folio(folio, new_folio, lruvec, list); > + > + /* Some pages can be beyond EOF: drop them from cache */ > + if (new_folio->index >= end) { > + if (shmem_mapping(mapping)) > + nr_shmem_dropped += > + folio_nr_pages(new_folio); Keep that on a single line. > + else if (folio_test_clear_dirty(new_folio)) > + folio_account_cleaned( > + new_folio, > + inode_to_wb(mapping->host)); > + __filemap_remove_folio(new_folio, NULL); > + folio_put_refs(new_folio, > + folio_nr_pages(new_folio)); > + } else if (mapping) { > + __xa_store(&mapping->i_pages, new_folio->index, > + new_folio, 0); > + } else if (swap_cache) { > + __xa_store(&swap_cache->i_pages, > + swap_cache_index(new_folio->swap), > + new_folio, 0); > + } > + } > + /* > + * Unfreeze @folio only after all page cache entries, which > + * used to point to it, have been updated with new folios. > + * Otherwise, a parallel folio_try_get() can grab origin_folio > + * and its caller can see stale page cache entries. > + */ > + folio_ref_unfreeze(folio, 1 + > + ((mapping || swap_cache) ? folio_nr_pages(folio) : 0)); Same as above probably. -- Cheers, David / dhildenb